Let's analyze the given pairs to determine if they represent pairs of isotopes:
### Pair (a): [tex]\( \text{11Na23} \)[/tex] and [tex]\( \text{11Na24} \)[/tex]
To determine if these two elements are isotopes, we need to check two main criteria:
1. They must have the same number of protons.
2. They must have different numbers of neutrons.
- Protons:
- Both elements are sodium (Na), which means they have the same number of protons.
- The atomic number for sodium (Na) is 11, so both elements have 11 protons.
- Neutrons:
- [tex]\( \text{11Na23} \)[/tex]
- Mass number = 23
- Number of neutrons = 23 (mass number) - 11 (protons) = 12 neutrons.
- [tex]\( \text{11Na24} \)[/tex]
- Mass number = 24
- Number of neutrons = 24 (mass number) - 11 (protons) = 13 neutrons.
The first element has 12 neutrons, and the second element has 13 neutrons.
Since they have the same number of protons (11) but different numbers of neutrons (12 and 13), these elements are isotopes of each other.
### Pair (b): [tex]\( \text{11Na24} \)[/tex] and [tex]\( \text{12Mg24} \)[/tex]
To determine if these two elements are isotopes, we again check the same criteria:
1. They must have the same number of protons.
2. They must have different numbers of neutrons.
- Protons:
- The first element is sodium (Na), so it has 11 protons.
- The second element is magnesium (Mg), which has an atomic number of 12, so it has 12 protons.
Since they have different numbers of protons (11 and 12), they cannot be isotopes. Isotopes must belong to the same element and therefore must have the same number of protons.
In summary:
- The pair [tex]\( 11\text{Na}23 \)[/tex] and [tex]\( 11\text{Na}24 \)[/tex] are isotopes.
- The pair [tex]\( 11\text{Na}24 \)[/tex] and [tex]\( 12\text{Mg}24 \)[/tex] are not isotopes.
